This invention relates to X-radiation sensitive thermally-developable imaging materials. In particular, this invention relates to X-radiation sensitive photothermographic materials containing X-radiation responsive phosphors that provide increased sensitivity (photographic speed). This invention also relates to methods of imaging using these photothermographic materials.
Silver-containing photothermographic imaging materials that are developed with heat and without liquid development have been known in the art for many years. Such materials are used in a recording process wherein an image is formed by imagewise exposure of the photothermographic material to specific electromagnetic radiation (for example, visible, ultraviolet, or infrared radiation) and developed by the use of thermal energy. These materials, also known as xe2x80x9cdry silverxe2x80x9d materials, generally comprise a support having coated thereon: (a) photosensitive catalyst (such as silver halide) that upon such exposure provides a latent image in exposed grains that are capable of acting as a catalyst for the subsequent formation of a silver image in a development step, (b) a non-photosensitive source of reducible silver ions, (c) a reducing composition (usually including a developer) for the reducible silver ions, and (d) a hydrophilic or hydrophobic binder. The latent image is then developed by application of thermal energy.
In such materials, the photosensitive catalyst is generally a photographic type photosensitive silver halide that is considered to be in catalytic proximity to the non-photosensitive source of reducible silver ions. Catalytic proximity requires intimate physical association of these two components either prior to or during the thermal image development process so that when silver atoms (Ag0)n, also known as silver specks, clusters, nuclei or latent image, are generated by irradiation or light exposure of the photosensitive silver halide, those silver atoms are able to catalyze the reduction of the reducible silver ions within a catalytic sphere of influence around the silver atoms [D. H. Klosterboer, Imaging Processes and Materials, (Neblette""s Eighth Edition), Sturge, Walworth and Shepp (Eds.), Van Nostrand-Reinhold, New York, Chapter 9, pp. 279-291, 1989]. It has long been understood that silver atoms act as a catalyst for the reduction of silver ions, and that the photosensitive silver halide can be placed in catalytic proximity with the non-photosensitive source of reducible silver ions in a number of different ways (see, for example, Research Disclosure, June 1978, item 17029). Other photosensitive materials, such as titanium dioxide, cadmium sulfide, and zinc oxide have also been reported to be useful in place of silver halide as the photocatalyst in photothermographic materials [see for example, Shepard, J. Appl. Photog. Eng. 1982, 8(5), 210-212, Shigeo et al., Nippon Kagaku Kaishi, 1994, 11, 992-997, and FR 2,254,047 (Robillard)].
The photosensitive silver halide may be made xe2x80x9cin situxe2x80x9d, for example by mixing an organic or inorganic halide-containing source with a source of reducible silver ions to achieve partial metathesis and thus causing the in-situ formation of silver halide (AgX) grains throughout the silver source [see, for example, U.S. Pat. No. 3,457,075 (Morgan et al.)]. In addition, photosensitive silver halides and sources of reducible silver ions can be coprecipitated [see Usanov et al., J. Imag. Sci. Tech. 1996, 40, 104]. Alternatively, a portion of the reducible silver ions can be completely converted to silver halide, and that portion can be added back to the source of reducible silver ions (see Usanov et al., International Conference on Imaging Science, Sep. 7-11, 1998).
The silver halide may also be xe2x80x9cpreformedxe2x80x9d and prepared by an xe2x80x9cex situxe2x80x9d process whereby the silver halide (AgX) grains are prepared and grown separately. With this technique, one has the possibility of controlling the grain size, grain size distribution, dopant levels, and composition much more precisely, so that one can impart more specific properties to both the silver halide grains and the photothermographic material. The preformed silver halide grains may be introduced prior to and be present during the formation of the source of reducible silver ions. Co-precipitation of the silver halide and the source of reducible silver ions provides a more intimate mixture of the two materials [see for example U.S. Pat. No. 3,839,049 (Simons)]. Alternatively, the preformed silver halide grains may be added to and physically mixed with the source of reducible silver ions.
The non-photosensitive source of reducible silver ions is a material that contains reducible silver ions. Typically, the preferred non-photosensitive source of reducible silver ions is a silver salt of a long chain aliphatic carboxylic acid having from 10 to 30 carbon atoms, or mixtures of such salts. Such acids are also known as xe2x80x9cfatty acidsxe2x80x9d or xe2x80x9cfatty carboxylic acidsxe2x80x9d. Silver salts of other organic acids or other organic compounds, such as silver imidazoles, silver tetrazoles, silver benzotriazoles, silver benzotetrazoles, silver benzothiazoles and silver acetylides have also been proposed. U.S. Pat. No. 4,260,677 (Winslow et al.) discloses the use of complexes of various inorganic or organic silver salts.
In photothermographic materials, exposure of the photographic silver halide to light produces small clusters containing silver atoms (Ag0)n. The imagewise distribution of these clusters, known in the art as a latent image, is generally not visible by ordinary means. Thus, the photosensitive material must be further developed to produce a visible image. This is accomplished by the reduction of silver ions that are in catalytic proximity to silver halide grains bearing the silver-containing-clusters of latent image. This produces a black-and-white image. The non-photosensitive silver source is catalytically reduced to form the visible black-and-white negative image while much of the silver halide, generally, remains as silver halide and is not reduced.
In photothermographic materials, the reducing agent for the reducible silver ions, often referred to as a xe2x80x9cdeveloperxe2x80x9d, may be any compound that, in the presence of the latent image, can reduce silver ion to metallic silver and is preferably of relatively low activity until it is heated to a temperature sufficient to cause the reaction. A wide variety of classes of compounds have been disclosed in the literature that function as developers for photothermographic materials. At elevated temperatures, the reducible silver ions are reduced by the reducing agent. Upon heating, this reaction occurs preferentially in the regions surrounding the latent image. This reaction produces a negative image of metallic silver having a color that ranges from yellow to deep black depending upon the presence of toning agents and other components in the imaging layer(s).
The imaging arts have long recognized that the field of photothermography is clearly distinct from that of photography. Photothermographic materials differ significantly from conventional silver halide photographic materials that require processing with aqueous processing solutions.
As noted above, in photothermographic imaging materials, a visible image is created by heat as a result of the reaction of a developer incorporated within the material. Heating at 50xc2x0 C. or more is essential for this dry development. In contrast, conventional photographic imaging materials require processing in aqueous processing baths at more moderate temperatures (from 30xc2x0 C. to 50xc2x0 C.) to provide a visible image.
In photothermographic materials, only a small amount of silver halide is used to capture light and a non-photosensitive source of reducible silver ions (for example, a silver carboxylate) is used to generate the visible image using thermal development. Thus, the imaged photosensitive silver halide serves as a catalyst for the physical development process involving the non-photosensitive source of reducible silver ions and the incorporated reducing agent. In contrast, conventional wet-processed, black-and-white photographic materials use only one form of silver (that is, silver halide) that, upon chemical development, is itself converted into the silver image, or that upon physical development requires addition of an external silver source (or other reducible metal ions that form black images upon reduction to the corresponding metal). Thus, photothermographic materials require an amount of silver halide per unit area that is only a fraction of that used in conventional wet-processed photographic materials.
Moreover, in photothermographic materials, all of the xe2x80x9cchemistryxe2x80x9d for imaging is incorporated within the material itself. For example, such materials include a developer (that is, a reducing agent for the reducible silver ions) while conventional photographic materials usually do not. Even in so-called xe2x80x9cinstant photographyxe2x80x9d, the developer chemistry is physically separated from the photosensitive silver halide until development is desired. The incorporation of the developer into photothermographic materials can lead to increased formation of various types of xe2x80x9cfogxe2x80x9d or other undesirable sensitometric side effects. Therefore, much effort has gone into the preparation and manufacture of photothermographic materials to minimize these problems during the preparation of the photothermographic emulsion as well as during coating, use, storage, and post-processing handling.
In addition, in photothermographic materials, the unexposed silver halide generally remains intact after development and the material must be stabilized against further imaging and development. In contrast, silver halide is removed from conventional photographic materials after solution development to prevent further imaging (that is, in the aqueous fixing step).
In photothermographic materials, the binder is capable of wide variation and a number of binders (both hydrophilic and hydrophobic) are useful. In contrast, conventional photographic materials are limited almost exclusively to hydrophilic colloidal binders such as gelatin.
Because photothermographic materials require dry thermal processing, they present distinctly different problems and require different materials in manufacture and use, compared to conventional, wet-processed silver halide photographic materials. Additives that have one effect in conventional silver halide photographic materials may behave quite differently when incorporated in photothermographic materials where the underlying chemistry is significantly more complex. The incorporation of such additives as, for example, stabilizers, antifoggants, speed enhancers, supersensitizers, and spectral and chemical sensitizers in conventional photographic materials is not predictive of whether such additives will prove beneficial or detrimental in photothermographic materials. For example, it is not uncommon for a photographic antifoggant useful in conventional photographic materials to cause various types of fog when incorporated into photothermographic materials, or for supersensitizers that are effective in photographic materials to be inactive in photothermographic materials.
These and other distinctions between photothermographic and photographic materials are described in Imaging Processes and Materials (Neblette""s Eighth Edition), noted above, Unconventional Imaging Processes, E. Brinckman et al. (Eds.), The Focal Press, London and New York, 1978, pp. 74-75, in Zou et al., J. Imaging Sci. Technol. 1996, 40, 94-103, and in M. R. V. Sahyun, J. Imaging Sci. Technol. 1998, 42, 23.
Problem to be Solved
Historically, photographic films containing various silver halides have been used for various radiographic purposes. Such films have exhibited excellent sensitivity to X-radiation, high spatial resolution, low image noise, and archival storage properties. Desired sensitivity to imaging X-radiation has been achieved through amplification of a relatively small number of latent image centers without too much xe2x80x9cnoisexe2x80x9d being added to the image. However, such films require the use of undesirable aqueous processing solutions and equipment.
The term xe2x80x9cnoisexe2x80x9d is understood in radiography to refer to the random variations in optical density throughout a radiographic image that impair the user""s ability to distinguish objects within the image. Radiographic noise is considered to have a number of components identified in the art as xe2x80x9cquantum mottlexe2x80x9d, film grain, and xe2x80x9cstructure mottlexe2x80x9d, as noted for example by Ter-Pogossian, The Physical Aspects of Diagnostic Radiology, Harper and Row, New York, Chapter 7, 1967.
Wet-processed radiographic films have generally been used in combination with some other material to convert X-radiation to another radiation form that can be more readily detected by silver halide in the films. Generally, such radiation xe2x80x9cconvertingxe2x80x9d materials are metal plates or metal oxides that convert X-radiation to electrons, or inorganic phosphors that convert X-radiation to visible radiation. Such xe2x80x9cconvertingxe2x80x9d materials are also usually provided in a separate element in what is known as xe2x80x9cmetal screensxe2x80x9d, xe2x80x9cintensifying screensxe2x80x9d or xe2x80x9cphosphor panelsxe2x80x9d because if phosphors or metal oxides are included within the typical silver halide emulsion, very high image noise levels result. This is due to the fact that electrons or visible radiation from the xe2x80x9cconvertingxe2x80x9d materials will expose many silver halide grains at the same time, including those outside of the xe2x80x9cimage areaxe2x80x9d. Upon development, the exposed silver halide grains are xe2x80x9ccorrelatedxe2x80x9d (that is, all the grains in the vicinity of the phosphor particle are developed, giving rise to high image noise. Thus, metal or phosphor intensifying screens or panels have been commonly used in combination with radiographic films in what are known as cassettes or radiographic imaging assemblies.
Attempts to incorporate phosphors in wet silver halide to improve sensitivity to X-radiation have been not been favored. K. Becker and coworkers found that incorporation of p-terphenyl into an wet silver halide emulsion gave a material with a flat energy response between 10 keV and 1000 keV but with an excessive amount of noise (K. Becker, E. Klein, and E. Zeitler, Naturwissen-schaften, 1960, 47, 199, K. Becker, Roentgenstr, 1961a, 95, 694, and K. Becker, Roentgenstr, 1961b, 95, 939).
Efforts have been made to achieve increased photographic speed in photothermographic materials because such materials offer a number of important advantages over the use of conventional wet-processed photographic materials. However, a significant problem with photothermographic materials is the difficulty in achieving high speed without accompanying increases in unwanted density (Dmin) or a loss in image contrast.
Another problem arises in such materials because the level of silver halide is relatively low compared to wet-processed photographic materials. Thus, direct exposure of such materials to X-radiation would require that a very high dosage be delivered to the film (through a patient) in order to produce a useful image. Obviously, this would be unacceptable for both human and animal subjects.
One approach to reducing the amount of X-radiation exposure needed to produce an image in photothermographic materials is to place xe2x80x9cdouble faced coatingsxe2x80x9d of photothermographic materials into contact with metal or phosphor intensifying screens [see for example JP Kokai 2001-109101 (Konica)]. Lamination of the phosphor screen to the photothermographic coating is described in JP Kokai 2001-022027 (Konica). However, there are imaging applications in which the use of such contact screens would be disadvantageous. For example, in the practice of intra-oral dental radiography, reuse of the expensive intensifying screens would require sterilization between uses. In addition, light spread and modulation transfer function (MTF) reducing characteristics associated with intensifying screens can reduce image sharpness to unacceptable levels.
Thus, as indicated in the previous discussion, there is a need for a way to render photothermographic materials X-radiation sensitive without a loss in photospeed or Dmax or a significant increase in fog (Dmin). There is also a need to achieve this X-radiation sensitivity in photothermographic materials without the use of heavy, bulky, and costly phosphor intensifying screens.
Screens that provide light output matched to the spectral sensitivity of the silver halide in the photothermographic materials would be especially useful.
The present invention provides an X-radiation sensitive photothermographic material comprising a support having on at least one side thereof, one or more imaging layers comprising a binder and in reactive association:
a. a photosensitive silver halide,
b. a non-photosensitive source of reducible silver ions,
c. a reducing composition for the reducible silver ions, and
d. a phosphor that is sensitive to X-radiation and is present in an amount of at least 0.1 mole per mole of total silver.
Further, a method of this invention for forming a visible image comprises:
A) imagewise exposing the photothermographic material described above to X-radiation to form a latent image, and
B) simultaneously or sequentially, heating the exposed photothermographic material to develop the latent image into a visible image.
Still again, the present invention provides an imaging precursor emulsion comprising the following component d in combination with any two or more of the following components a, b, and c:
a. a photosensitive silver halide,
b. a non-photosensitive source of reducible silver ions,
c. a reducing composition for the reducible silver ions, and
d. a phosphor that is sensitive to X-radiation.
We have unexpectedly found that the addition of phosphors to the imaging layers (or adjacent layers) of photothermographic materials provides an increase in sensitivity to X-radiation. Moreover, we have also found that placing phosphors in reactive association with the photosensitive silver halide provides high resolution, image sharpness, and a low level of xe2x80x9cnoisexe2x80x9d and image fog. A relatively small amount of phosphor is needed to provide these benefits.
The present invention further provides an X-radiation sensitive photothermographic material comprising a support having on both sides thereof, one or more of the same or different imaging layers comprising a binder and in reactive association:
a. a photosensitive silver halide,
b. a non-photosensitive source of reducible silver ions,
c. a reducing composition for the reducible silver ions, and
d. a phosphor that is sensitive to X-radiation and is present in an amount of at least 0.1 mole per mole of total silver.
We have also found when photothermographic films incorporating phosphors within the imaging layers (or adjacent layers) are placed in contact with X-ray screens a further increase in sensitivity to X-radiation occurs.
The photothermographic materials of this invention can be used, for example, in conventional black-and-white or color photothermography, in electronically generated black-and-white or color hardcopy recording. The imaging precursor emulsions and photothermographic materials of the present invention are preferably used to obtain black-and-white images.
The photothermographic materials of this invention are particularly useful for medical imaging of human or animal subjects in response to X-radiation. Such applications include, but are not limited to, thoracic imaging, mammography, dental imaging, orthopedic imaging, general medical radiography, therapeutic radiography, veterinary radiography, and autoradiography. The materials are also particularly useful for various non-medical uses of X-radiation, for example in X-ray lithography and industrial radiographic applications such the nondestructive testing of welds and for minute flaws which could affect performance.
It is particularly desirable to use the photothermographic materials of this invention to provide black-and-white images of human or animal subjects.
In the photothermographic materials of this invention, the components necessary for imaging can be in one or more layers. The layer(s) that contain a photosensitive silver halide and non-photosensitive source of reducible silver ions, or both, are referred to herein as emulsion layer(s). The photosensitive silver halide and the non-photosensitive source of reducible silver ions are in catalytic proximity and preferably in the same emulsion layer. In addition, the one or more phosphors described herein are also in catalytic proximity or reactive association with the photosensitive silver halide, and are preferably in the same emulsion layer.
Various other layers are usually disposed on the xe2x80x9cbacksidexe2x80x9d (non-emulsion side) of the materials, including antihalation layer(s), protective layers, antistatic layers, conducting layers, and transport enabling layers.
Various layers are also usually disposed on the xe2x80x9cfrontsidexe2x80x9d or emulsion side of the support, including protective topcoat layers, primer layers, interlayers, opacifying layers, antistatic layers, antihalation layers, acutance layers, auxiliary layers, and others readily apparent to one skilled in the art.
The present invention also provides a process for the formation of a visible image (usually a black-and-white image) by first exposing to X-radiation and thereafter heating the inventive photothermographic material. In one embodiment, the present invention provides a process comprising:
A) imagewise exposing the photothermographic material of this invention to X-radiation to generate a latent image, and
B) simultaneously or sequentially, heating the exposed photothermographic material to develop the latent image into a visible image.
When the photothermographic materials of this invention are heat-developed as described below in a substantially water-free condition after, or simultaneously with, imagewise exposure, a silver image (preferably a black-and-white silver image) is obtained.
Definitions
As used herein:
In the descriptions of the photothermographic materials of the present invention, xe2x80x9caxe2x80x9d or xe2x80x9canxe2x80x9d component refers to xe2x80x9cat least onexe2x80x9d of that component. For example, the phosphors described herein can be used individually or in mixtures.
Heating in a substantially water-free condition as used herein, means heating at a temperature of from about 50xc2x0 to about 250xc2x0 C. with little more than ambient water vapor present. The term xe2x80x9csubstantially water-free conditionxe2x80x9d means that the reaction system is approximately in equilibrium with water in the air and water for inducing or promoting the reaction is not particularly or positively supplied from the exterior to the material. Such a condition is described in T. H. James, The Theory of the Photographic Process, Fourth Edition, Macmillan 1977, page 374.
xe2x80x9cPhotothermographic material(s)xe2x80x9d means a construction comprising at least one photothermographic emulsion layer or a photothermographic set of layers (wherein the silver halide and the source of reducible silver ions are in one layer and the other essential components, including the phosphor, or desirable additives are distributed, as desired, in an adjacent coating layer) and any supports, topcoat layers, image-receiving layers, blocking layers, antihalation layers, subbing or priming layers. These materials also include multilayer constructions in which one or more imaging components are in different layers, but are in xe2x80x9creactive associationxe2x80x9d so that they readily come into contact with each other during imaging and/or development. For example, one layer can include the non-photosensitive source of reducible silver ions and another layer can include the reducing composition, but the two reactive components are in reactive association with each other.
xe2x80x9cEmulsion layerxe2x80x9d, xe2x80x9cimaging layerxe2x80x9d, or xe2x80x9cphotothermographic emulsion layerxe2x80x9d, means a layer of a photothermographic material that contains the photosensitive silver halide and/or non-photosensitive source of reducible silver ions. It can also mean a layer of the photothermographic material that contains, in addition to the photosensitive silver halide and/or non-photosensitive source of reducible ions, additional essential imaging components (such as the phosphor) and/or desirable additives. These layers are usually on what is known as the xe2x80x9cfrontsidexe2x80x9d of the support, but in some embodiments can be on both the frontside and backside of the support.
The four xe2x80x9cessential imaging componentsxe2x80x9d required in the photothermographic materials of this invention are the photosensitive silver halide, a non-photosensitive source of reducible silver ions, a reducing composition for the reducible silver ions, and a phosphor. All of these essential imaging components are incorporated into one or more layers of the photothermographic materials during manufacture. In other words, they are not incorporated from an external source has as a laminated element or phosphor screen.
An xe2x80x9cimaging precursor emulsionxe2x80x9d refers herein to a formulation that includes one or more phosphors and two or more of the three other essential components. In other words, an xe2x80x9cimaging precursor emulsionxe2x80x9d can include any three or all four of the essential components as long as the phosphor is present.
xe2x80x9cUltraviolet region of the spectrumxe2x80x9d refers to that region of the spectrum less than or equal to 410 nm, and preferably from about 100 nm to about 410 nm, although parts of these ranges may be visible to the naked human eye. More preferably, the ultraviolet region of the spectrum is the region of from about 190 to about 405 nm.
xe2x80x9cShort wavelength visible region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 400 nm to about 450 nm.
xe2x80x9cVisible region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 400 nm to about 700 nm.
xe2x80x9cRed region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 600 nm to about 700 nm.
xe2x80x9cInfrared region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 700 nm to about 1400 nm.
xe2x80x9cMiddle chalcogenxe2x80x9d means sulfur (S), selenium (Se), or tellurium (Te).
xe2x80x9cNon-photosensitivexe2x80x9d means not intentionally light sensitive.
xe2x80x9cTransparentxe2x80x9d means capable of transmitting visible light or imaging radiation without appreciable scattering or absorption.
A xe2x80x9cphosphorxe2x80x9d is an inorganic compound that is responsive to X-radiation and upon irradiation, emits radiation in the ultraviolet, visible, or infrared region of the spectrum. Most phosphors emit such radiation immediately upon exposure to stimulating radiation. However, some phosphors are known as xe2x80x9cstoragexe2x80x9d phosphors because they have the capacity to store energy from the initial irradiation and to release the light at a later time when stimulated by still other radiation.
The term xe2x80x9cRADxe2x80x9d is used to indicate a unit dose of absorbed radiation, that is energy absorption of 100 ergs per gram of tissue.
The terms xe2x80x9ckVpxe2x80x9d and xe2x80x9cMVpxe2x80x9d stand for peak voltage applied to an X-ray tube times 103 and 106, respectively.
The term xe2x80x9crare earthxe2x80x9d is used to indicate elements having an atomic number of 39 or 57 through 71.
The term xe2x80x9cdouble-sided coatingxe2x80x9d or xe2x80x9cdouble-faced coatingxe2x80x9d is used to define an imaging material having the same or different photothermographic imaging or emulsion layers disposed on both the front- and backsides of the support.
As is well understood in this area, for compounds useful herein, substitution is not only tolerated, but is often advisable and various substituents are anticipated on the compounds used in the present invention. Thus, when a compound is referred to as xe2x80x9chaving the structurexe2x80x9d of a given formula, any substitution that does not alter the bond structure of the formula or the shown atoms within that structure is included within the formula, unless such substitution is specifically excluded by language (such as xe2x80x9cfree of carboxy-substituted alkylxe2x80x9d). For example, where a benzene ring structure is shown (including fused ring structures), substituent groups may be placed on the benzene ring structure, but the atoms making up the benzene ring structure may not be replaced.
As a means of simplifying the discussion and recitation of certain substituent groups, the term xe2x80x9cgroupxe2x80x9d refers to chemical species that may be substituted as well as those that are not so substituted. Thus, the term xe2x80x9cgroupxe2x80x9d, such as xe2x80x9calkyl groupxe2x80x9d is intended to include not only pure hydrocarbon alkyl chains, such as methyl, ethyl, propyl, t-butyl, cyclohexyl, iso-octyl, octadecyl and the like, but also alkyl chains bearing substituents known in the art, such as hydroxyl, alkoxy, phenyl, halogen atoms (F, Cl, Br, and I), cyano, nitro, amino, carboxy and the like. For example, alkyl group includes ether and thioether groups (for example, CH3xe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94CH2xe2x80x94 or CH3xe2x80x94CH2xe2x80x94CH2xe2x80x94Sxe2x80x94CH2xe2x80x94), haloalkyl, nitroalkyl, carboxyalkyl, hydroxyalkyl, sulfoalkyl, and other groups readily apparent to one skilled in the art. Substituents that adversely react with other active ingredients, such as very strongly electrophilic or oxidizing substituents, would, of course, be excluded by the ordinarily skilled artisan as not being inert or harmless.
Research Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also available from Emsworth Design Inc., 147 West 24th Street, New York, N.Y. 10011).
Other aspects, advantages, and benefits of the present invention are apparent from the detailed description, examples, and claims provided in this application.
The Photosensitive Silver Halide
As noted above, the photothermographic materials of the present invention include one or more photosensitive silver halides such as silver bromide, silver iodide, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide, and others readily apparent to one skilled in the art. Mixtures of photosensitive silver halides can also be used in any suitable proportion. Silver bromide and silver bromoiodide are more preferred, with the latter silver halide having up to 10 mol % silver iodide. Typical techniques for preparing and precipitating silver halide grains are described in Research Disclosure, 1978, Item 17643.
The shape of the photosensitive silver halide grains used in the present invention is in no way limited. The silver halide grains may have any crystalline habit including, but not limited to, cubic, octahedral, rhombic, dodecahedral, orthorhombic, tetrahedral, other polyhedral, laminar, twinned, platelet, or tabular morphologies and may have epitaxial growth of crystals thereon. If desired, a mixture of these crystals can be employed. Silver halide grains having cubic or tabular morphology are preferred.
The photosensitive silver halide grains may have a uniform ratio of halide throughout. They may have a graded halide content, with a continuously varying ratio of, for example, silver bromide and silver iodide or they may be of the core-shell type, having a discrete core of one halide ratio, and a discrete shell of another halide ratio. Core-shell silver halide grains useful in photothermographic materials and methods of preparing these materials are described for example in U.S. Pat. No. 5,382,504 (Shor et al.), incorporated herein by reference. Iridium and/or copper doped core-shell and non-core-shell grains are described in U.S. Pat. No. 5,434,043 (Zou et al.) and U.S. Pat. No. 5,939,249 (Zou), incorporated herein by reference.
The photosensitive silver halide can be added to (or formed within) the emulsion layer(s) in any fashion as long as it is placed in catalytic proximity to the non-photosensitive source of reducible silver ions.
It is preferred that the silver halides be preformed and prepared by an ex-situ process. The silver halide grains prepared ex-situ may then be added to and physically mixed with the non-photosensitive source of reducible silver ions. It is more preferable to form the source of reducible silver ions in the presence of ex-situ-prepared silver halide. In this process, the source of reducible silver ions, such as a long chain fatty acid silver carboxylate (commonly referred to as a silver xe2x80x9csoapxe2x80x9d), is formed in the presence of the preformed silver halide grains. Co-precipitation of the reducible source of silver ions in the presence of silver halide provides a more intimate mixture of the two materials [see, for example U.S. Pat. No. 3,839,049 (Simons)]. Materials of this type are often referred to as xe2x80x9cpreformed soapsxe2x80x9d.
Preformed silver halide emulsions used in the materials of this invention can be prepared by aqueous or organic processes and can be unwashed or washed to remove soluble salts. In the latter case, the soluble salts can be removed by ultrafiltration, by chill setting and leaching, or by washing the coagulum [for example, by the procedures described in U.S. Pat. No. 2,618,556 (Hewitson et al.), U.S. Pat. No. 2,614,928 (Yutzy et al.), U.S. Pat. No. 2,565,418 (Yackel), U.S. Pat. No. 3,241,969 (Hart et al.), and U.S. Pat. No. 2,489,341 (Waller et al.), all incorporated herein by reference].
It is also effective to use an in situ process in which a halide-containing compound is added to an organic silver salt to partially convert the silver of the organic silver salt to silver halide. The halogen-containing compound can be inorganic (such as zinc bromide or lithium bromide) or organic (such as N-bromosuccinimide).
Additional methods of preparing these silver halide and organic silver salts and manners of blending them are described in Research Disclosure, June 1978, item 17029, U.S. Pat. No. 3,700,458 (Lindholm) and U.S. Pat. No. 4,076,539 (Ikenoue et al.), and JP Applications 13224/74, 42529/76, and 17216/75, all incorporated herein by reference.
A preferred method of making photosensitive silver halide grains is described in copending and commonly assigned U.S. Ser. No. 09/833,533 (filed Apr. 12, 2001 by Shor, Zou, Ulrich, and Simpson), in which the silver halide grains are prepared in the presence of a hydroxytetrazaindene or N-heterocyclic compound comprising a mercapto group (such as 1-phenyl-5-mercaptotetrazole). This application is incorporated herein by reference.
The photosensitive silver halide grains used in the present invention can vary in average diameter of up to several micrometers (xcexcm) depending on their desired use. Preferred silver halide grains are those having an average particle size of from about 0.01 to about 1.5 xcexcm, more preferred are those having an average particle size of from about 0.03 to about 1.0 xcexcm, and most preferred are those having an average particle size of from about 0.05 to about 0.8 xcexcm. Those of ordinary skill in the art understand that there is a finite lower practical limit for silver halide grains that is partially dependent upon the wavelengths to which the grains are spectrally sensitized. Such a lower limit, for example, is typically from about 0.01 to about 0.005 xcexcm.
The average size of the photosensitive silver halide grains is expressed by the average diameter if the grains are spherical, and by the average of the diameters of equivalent circles for the projected images if the grains are cubic or in other non-spherical shapes.
Grain size may be determined by any of the methods commonly employed in the art for particle size measurement. Representative methods are described by in xe2x80x9cParticle Size Analysisxe2x80x9d, ASTM Symposium on Light Microscopy, R. P. Loveland, 1955, pp. 94-122, and in C. E. K. Mees and T. H. James, The Theory of the Photographic Process, Third Edition, Chapter 2, Macmillan Company, 1966. Particle size measurements may be expressed in terms of the projected areas of grains or approximations of their diameters. These will provide reasonably accurate results if the grains of interest are substantially uniform in shape.
The one or more photosensitive silver halides used in the photothermographic materials of the present invention are preferably present in an amount of from about 0.005 to about 0.5 mole, more preferably from about 0.01 to about 0.25 mole per mole, and most preferably from about 0.03 to about 0.15 mole, per mole of non-photosensitive source of reducible silver ions.
Chemical and Spectral Sensitizers
The photosensitive silver halides used in this invention may be employed without modification. However, they are preferably chemically and/or spectrally sensitized in a manner similar to that used to sensitize conventional wet-processed silver halide photographic materials or state-of-the-art heat-developable photothermographic materials.
Thus, the photosensitive silver halides may be chemically sensitized with one or more chemical sensitizing agents, such as a compound containing sulfur, selenium, or tellurium, or with a compound containing gold, platinum, palladium, ruthenium, rhodium, iridium, or combinations thereof, a reducing agent such as a tin halide or a combination of any of these. The details of these procedures are described in T. H. James, The Theory of the Photographic Process, Fourth Edition, Chapter 5, pp. 149-169. Suitable chemical sensitization procedures are also disclosed in U.S. Pat. No. 1,623,499 (Sheppard et al.), U.S. Pat. No. 2,399,083 (Waller et al.), U.S. Pat. No. 3,297,447 (McVeigh), U.S. Pat. No. 3,297,446 (Dunn), U.S. Pat. No. 5,049,485 (Deaton), U.S. Pat. No. 5,252,455 (Deaton), U.S. Pat. No. 5,391,727 (Deaton), U.S. Pat. No. 5,912,111 (Lok et al.), U.S. Pat. No. 5,759,761 (Lushington et al.), and EP-A-0 915 371 (Lok et al.), all incorporated herein by reference. Mixtures of one or more types of chemical sensitizing agents can also be used.
One method of chemical sensitization is by oxidative decomposition of a spectral sensitizing dye in the presence of a photothermographic emulsion, as described in U.S. Pat. No. 5,891,615 (Winslow et al.), incorporated herein by reference.
Sulfur-containing chemical sensitizers useful in the present invention are well known in the art and described for example, in Sheppard et al., J. Franklin Inst., 1923, 196, pp. 653 and 673, C. E. K. Mees and T. H. James, The Theory of the Photographic Process, 4th Edition, 1977, pp. 152-3, Tani, T., Photographic Sensitivity: Theory and Mechanisms, Oxford University Press, NY, 1995, pp. 167-176, U.S. Pat. No. 5,891,615 (Winslow et al.), Zavlin et al., ISandT""s 48th Annual Conference Papers, May 7-11, 1995 Washington D.C., pp. 156-6), U.S. Pat. No. 4,810,626 (Burgmaier et al.), U.S. Pat. No. 4,036,650 (Kobayashi et al.), U.S. Pat. No. 4,213,784 (Ikenoue et al.), and U.S. Pat. No. 4,207,108 (Hiller), all incorporated herein by reference.
Particularly useful sulfur-containing chemical sensitizers are tetrasubstituted thiourea compounds, preferably such thiourea compounds that are substituted with the same or different aliphatic substituents, and more preferably, those that are substituted with the same aliphatic substituent. Such useful thioureas are described for example in U.S. Pat. No. 5,843,632 (Eshelman et al.) and in copending and commonly assigned U.S. Ser. No. 09/667,748 (filed Sep. 21, 2000 by Lynch, Simpson, Shor, Willett, and Zou), incorporated herein by reference.
Particularly, useful tellurium-containing chemical sensitizing compounds are described in copending and commonly assigned U.S. Ser. No. 09/746,400 (filed Dec. 21, 2000 by Lynch, Opatz, Shor, Simpson, Willett, and Gysling), incorporated herein by reference.
Useful combinations of sulfur- or tellurium-containing chemical sensitizers with gold(III) chemical sensitizers are described in copending and commonly assigned U.S. Ser. No. 09/768,094 (filed Jan. 24, 2001 by Simpson, Whitcomb, and Shor), incorporated herein by reference.
The total amount of chemical sensitizers that may be used during formulation of the imaging composition will generally vary depending upon the average size of silver halide grains. The total amount is generally at least 10xe2x88x9210 mole per mole of total silver, and preferably from 10xe2x88x928 to about 10xe2x88x922 mole per mole of total silver for silver halide grains having an average size of from about 0.01 to about 2 xcexcm. The upper limit can vary depending upon the compound used, the level of silver halide and the average grain size, and it would be readily determinable by one of ordinary skill in the art.
In general, it may also be desirable to add spectral sensitizing dyes to one or more imaging layers to enhance silver halide sensitivity to ultraviolet, visible and infrared light. Thus, the photosensitive silver halides may be spectrally sensitized with various dyes that are known to spectrally sensitize silver halide. Non-limiting examples of sensitizing dyes that can be employed include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes, and hemioxanol dyes. The cyanine dyes, merocyanine dyes and complex merocyanine dyes are particularly useful. Suitable sensitizing dyes such as those described in U.S. Pat. No. 3,719,495 (Lea), U.S. Pat. No. 5,393,654 (Burrows et al.), U.S. Pat. No. 5,441,866 (Miller et al.), U.S. Pat. No. 5,541,054 (Miller et al.), U.S. Pat. No. 5,281,515 (Delprato et al.), and U.S. Pat. No. 5,314,795 (Helland et al.), all incorporated herein by reference, are effective in the practice of the invention.
An appropriate amount of spectral sensitizing dye added is generally about 10xe2x88x9210 to 10xe2x88x921 mole, and preferably, about 10xe2x88x927 to 10xe2x88x922 mole per mole of silver halide.
To further control the properties of photothermographic materials, (for example, contrast, Dmin, or fog), it may be preferable to add one or more heteroaromatic mercapto compounds or heteroaromatic disulfide compounds as xe2x80x9csupersensitizersxe2x80x9d. Examples include compounds of the formulae: Arxe2x80x94Sxe2x80x94M and Arxe2x80x94Sxe2x80x94Sxe2x80x94Ar, wherein M represents a hydrogen atom or an alkali metal atom and Ar represents a heteroaromatic ring or fused heteroaromatic ring containing one or more of nitrogen, sulfur, oxygen, selenium, or tellurium atoms. Preferably, the heteroaromatic ring comprises benzimidazole, naphthimidazole, benzothiazole, naphthothiazole, benzoxazole, naphthoxazole, benzoselenazole, benzotellurazole, imidazole, oxazole, pyrazole, triazole, thiazole, thiadiazole, tetrazole, triazine, pyrimidine, pyridazine, pyrazine, pyridine, purine, quinoline, or quinazolinone. Compounds having other heteroaromatic rings and compounds providing enhanced sensitization at other wavelengths are also envisioned to be suitable. Many of the above compounds are described in EP-A-0 559 228 (Philip Jr. et al.) as supersensitizers for infrared photothermographic materials.
The heteroaromatic ring may also carry substituents. Examples of preferred substituents are halo groups (such as bromo and chloro), hydroxy, amino, carboxy, alkyl groups (for example, of 1 or more carbon atoms and preferably 1 to 4 carbon atoms), and alkoxy groups (for example, of 1 or more carbon atoms and preferably of 1 to 4 carbon atoms).
Heteroaromatic mercapto compounds are most preferred. Examples of preferred heteroaromatic mercapto compounds are 2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole, 2-mercaptobenzothiazole and 2-mercaptobenzoxazole, and mixtures thereof.
If used, a heteroaromatic mercapto compound is generally present in an emulsion layer in an amount of at least about 0.0001 mole per mole of total silver in the emulsion layer. More preferably, the heteroaromatic mercapto compound is present within a range of about 0.001 mole to about 1.0 mole, and most preferably, about 0.005 mole to about 0.2 mole, per mole of total silver.
Non-Photosensitive Source of Reducible Silver Ions
The non-photosensitive source of reducible silver ions used in photothermographic materials of the present invention can be any compound that contains reducible silver (1+) ions in catalytic association with the photosensitive silver halide. Preferably, it is a silver salt that is comparatively stable to light and forms a silver image when heated to 50xc2x0 C. or higher in the presence of an exposed photosensitive silver halide and a reducing agent composition.
Silver salts of organic acids, particularly silver salts of long-chain carboxylic acids are preferred. The chains typically contain 10 to 30, and preferably 15 to 28, carbon atoms. Suitable organic silver salts include silver salts of organic compounds having a carboxylic acid group. Examples thereof include a silver salt of an aliphatic carboxylic acid or a silver salt of an aromatic carboxylic acid. Preferred examples of the silver salts of aliphatic carboxylic acids include silver behenate, silver arachidate, silver stearate, silver oleate, silver laurate, silver caprate, silver myristate, silver palmitate, silver maleate, silver fumarate, silver tartarate, silver furoate, silver linoleate, silver butyrate, silver camphorate, and mixtures thereof. Most preferably, at least silver behenate is present as the non-photosensitive source of reducible silver ions.
Preferred examples of the silver salts of aromatic carboxylic acid and other carboxylic acid group-containing compounds include, but are not limited to, silver benzoates, a silver substituted-benzoate, such as silver 3,5-dihydroxybenzoate, silver o-methylbenzoate, silver m-methylbenzoate, silver p-methylbenzoate, silver 2,4-dichlorobenzoate, silver acetamidobenzoate, silver p-phenylbenzoate, silver gallate, silver tannate, silver phthalate, silver terephthalate, silver salicylate, silver phenylacetate, silver pyromellitate, a silver salt of 3-carboxymethyl-4-methyl-4-thiazoline-2-thione or others as described in U.S. Pat. No. 3,785,830 (Sullivan et al.), and silver salts of aliphatic carboxylic acids containing a thioether group as described in U.S. Pat. No. 3,330,663 (Weyde et al.). Soluble silver carboxylates comprising hydrocarbon chains incorporating ether or thioether linkages, or sterically hindered substitution in the xcex1- (on a hydrocarbon group) or ortho- (on an aromatic group) position, and displaying increased solubility in coating solvents and providing coatings with less light scattering can also be used. Such silver carboxylates are described in U.S. Pat. No. 5,491,059 (Whitcomb). Mixtures of any of the silver salts described herein can also be used if desired.
Silver salts of sulfonates are also useful in the practice of this invention. Such materials are described for example in U.S. Pat. No. 4,504,575 (Lee). Silver salts of sulfosuccinates are also useful as described for example in EP-A-0 227 141 (Leenders et al.).
Silver salts of compounds containing mercapto or thione groups and derivatives thereof can also be used. Preferred examples of these compounds include, but are not limited to, a silver salt of 3-mercapto-4-phenyl-1,2,4-triazole, a silver salt of 2-mercaptobenzimidazole, a silver salt of 2-mercapto-5-amino-thiadiazole, a silver salt of 2-(2-ethylglycolamido)benzothiazole, silver salts of thioglycolic acids (such as a silver salt of a S-alkylthioglycolic acid, wherein the alkyl group has from 12 to 22 carbon atoms), silver salts of dithiocarboxylic acids (such as a silver salt of dithioacetic acid), a silver salt of thioamide, a silver salt of 5-carboxylic-1-methyl-2-phenyl-4-thiopyridine, a silver salt of mercaptotriazine, a silver salt of 2-mercaptobenzoxazole, silver salts as described in U.S. Pat. No. 4,123,274 (Knight et al.) (for example, a silver salt of a 1,2,4-mercaptothiazole derivative, such as a silver salt of 3-amino-5-benzylthio-1,2,4-thiazole), and a silver salt of thione compounds [such as a silver salt of 3-(2-carboxyethyl)-4-methyl-4-thiazoline-2-thione as described in U.S. Pat. No. 3,201,678 (Meixell)].
Furthermore, a silver salt of a compound containing an imino group can be used. Preferred examples of these compounds include, but are not limited to, silver salts of benzotriazole and substituted derivatives thereof (for example, silver methylbenzotriazole and silver 5-chlorobenzotriazole), silver salts of 1,2,4-triazoles or 1-H-tetrazoles such as phenylmercaptotetrazole as described in U.S. Pat. No. 4,220,709 (deMauriac), and silver salts of imidazoles and imidazole derivatives as described in U.S. Pat. No. 4,260,677 (Winslow et al.). Moreover, silver salts of acetylenes can also be used as described, for example in U.S. Pat. No. 4,761,361 (Ozaki et al.) and U.S. Pat. No. 4,775,613 (Hirai et al.).
It is also convenient to use silver half soaps. A preferred example of a silver half soap is an equimolar blend of silver carboxylate and carboxylic acid, which analyzes for about 14.5% by weight solids of silver in the blend and which is prepared by precipitation from an aqueous solution of the sodium salt of a commercial fatty carboxylic acid, or by addition of the free fatty acid to the silver soap. For transparent films a silver carboxylate full soap, containing not more than about 15% of free carboxylic acid and analyzing for about 22% silver, can be used. For opaque photothermographic materials, different amounts can be used.
Non-photosensitive sources of reducible silver ions can also be provided as core-shell silver salts such as those described in commonly assigned and copending U.S. Ser. No. 09/761,954 (filed Jan. 17, 2001 by Whitcomb and Pham), incorporated herein by reference. These silver salts include a core comprised of one or more silver salts and a shell having one or more different silver salts.
Still another useful source of non-photosensitive reducible silver ions in the practice of this invention are the silver dimer compounds that comprise two different silver salts as described in copending U.S. Ser. No. 09/812,597 (filed Mar. 20, 2001 by Whitcomb), incorporated herein by reference. Such non-photosensitive silver dimer compounds comprise two different silver salts, provided that when the two different silver salts comprise straight-chain, saturated hydrocarbon groups as the silver coordinating ligands, those ligands differ by at least 6 carbon atoms.
The methods used for making silver soap dispersions are well known in the art and are disclosed in Research Disclosure, April 1983, item 22812, Research Disclosure, October 1983, item 23419, U.S. Pat. No. 3,985,565 (Gabrielsen et al.) and the references cited above.
The one or more non-photosensitive sources of reducible silver ions are preferably present in an amount of about 5% by weight to about 70% by weight, and more preferably, about 10% to about 50% by weight, based on the total dry weight of the emulsion layer. Stated another way, the amount of the sources of reducible silver ions is generally present in an amount of from about 0.001 to about 0.2 mol/m2 of the dry photothermographic material, and preferably from about 0.01 to about 0.05 mol/m2 of that material.
The total amount of silver (from all silver sources) in the photothermographic materials is generally at least 0.002 mol/m2 and preferably from about 0.01 to about 0.05 mol/m2.
Phosphors
Phosphors are materials that emit infrared, visible, or ultraviolet radiation upon excitation. An intrinsic phosphor is a material that is naturally (that is, intrinsically) phosphorescent. An xe2x80x9cactivatedxe2x80x9d phosphor is one composed of a basic material which may or may not be an intrinsic phosphor, to which one or more dopant(s) has been intentionally added. These dopants xe2x80x9cactivatexe2x80x9d the phosphor and cause it to emit infrared, visible, or ultraviolet radiation. For example, in Gd2O2S:Tb, the Tb atoms (the dopant/activator) give rise to the optical emission of the phosphor. Some phosphors, such as BaFBr, are known as storage phosphors. In these materials, the dopants are involved in the storage as well as the emission of radiation.
Any conventional or useful phosphor can be used, singly or in mixtures, in the practice of this invention. More specific details of useful phosphors are provided as follows.
For example, useful phosphors are described in numerous references relating to fluorescent intensifying screens, including but not limited to, Research Disclosure, Vol. 184, August 1979, Item 18431, Section IX, X-ray Screens/Phosphors, and U.S. Pat. No. 2,303,942 (Wynd et al.), U.S. Pat. No. 3,778,615 (Luckey), U.S. Pat. No. 4,032,471 (Luckey), U.S. Pat. No. 4,225,653 (Brixner et al.), U.S. Pat. No. 3,418,246 (Royce), U.S. Pat. No. 3,428,247 (Yocon), U.S. Pat. No. 3,725,704 (Buchanan et al.), U.S. Pat. No. 2,725,704 (Swindells), U.S. Pat. No. 3,617,743 (Rabatin), U.S. Pat. No. 3,974,389 (Ferri et al.), U.S. Pat. No. 3,591,516 (Rabatin), U.S. Pat. No. 3,607,770 (Rabatin), U.S. Pat. No. 3,666,676 (Rabatin), U.S. Pat. No. 3,795,814 (Rabatin), U.S. Pat. No. 4,405,691 (Yale), U.S. Pat. No. 4,311,487 (Luckey et al.), U.S. Pat. No. 4,387,141 (Patten), U.S. Pat. No. 5,021,327 (Bunch et al.), U.S. Pat. No. 4,865,944 (Roberts et al.), U.S. Pat. No. 4,994,355 (Dickerson et al.), U.S. Pat. No. 4,997,750 (Dickerson et al.), U.S. Pat. No. 5,064,729 (Zegarski), U.S. Pat. No. 5,108,881 (Dickerson et al.), U.S. Pat. No. 5,250,366 (Nakajima et al.), U.S. Pat. No. 5,871,892 (Dickerson et al.), EP-A-0 491,116 (Benzo et al.), the disclosures of all of which are incorporated herein by reference with respect to the phosphors.
Useful classes of phosphors include, but are not limited to, calcium tungstate (CaWO4), activated or unactivated lithium stannates, niobium and/or rare earth activated or unactivated yttrium, lutetium, or gadolinium tantalates, rare earth (such as terbium, lanthanum, gadolinium, cerium, and lutetium)-activated or unactivated middle chalcogen phosphors such as rare earth oxychalcogenides and oxyhalides, and terbium-activated or unactivated lanthanum and lutetium middle chalcogen phosphors.
Still other useful phosphors are those containing hafnium as described for example in U.S. Pat. No. 4,988,880 (Bryan et al.), U.S. Pat. No. 4,988,881 (Bryan et al.), U.S. Pat. No. 4,994,205 (Bryan et al.), U.S. Pat. No. 5,095,218 (Bryan et al.), U.S. Pat. No. 5,112,700 (Lambert et al.), U.S. Pat. No. 5,124,072 (Dole et al.), and U.S. Pat. No. 5,336,893 (Smith et al.), the disclosures of which are all incorporated herein by reference.
Preferred rare earth oxychalcogenide and oxyhalide phosphors are represented by the following formula (1):
Mxe2x80x2(wxe2x88x92n)Mxe2x80x3nOwXxe2x80x2xe2x80x83xe2x80x83(1)
wherein Mxe2x80x2 is at least one of the metals yttrium (Y), lanthanum (La), gadolinium (Gd), or lutetium (Lu), Mxe2x80x3 is at least one of the rare earth metals, preferably dysprosium (Dy), erbium (Er), europium (Eu), holmium (Ho), neodymium (Nd), praseodymium (Pr), samarium (Sm), tantalum (Ta), terbium (Tb), thulium (Tm), or ytterbium (Yb), Xxe2x80x2 is a middle chalcogen (S, Se, or Te) or halogen, n is 0.002 to 0.2, and w is 1 when Xxe2x80x2 is halogen or 2 when Xxe2x80x2 is a middle chalcogen. These include rare earth-activated lanthanum oxybromides, and terbium-activated or thulium-activated gadolinium oxides such as Gd2O2S:Tb.
Other suitable phosphors are described in U.S. Pat. No. 4,835,397 (Arakawa et al.) and U.S. Pat. No. 5,381,015 (Dooms), both incorporated herein by reference, and including for example divalent europium and other rare earth activated alkaline earth metal halide phosphors and rare earth element activated rare earth oxyhalide phosphors. Of these types of phosphors, the more preferred phosphors include alkaline earth metal fluorohalide prompt emitting and/or storage phosphors [particularly those containing iodide such as alkaline earth metal fluorobromoiodide storage phosphors as described in U.S. Pat. No. 5,464,568 (Bringley et al.), incorporated herein by reference].
Another class of phosphors are those that include a rare earth host and are rare earth activated mixed alkaline earth metal sulfates such as europium-activated barium strontium sulfate.
Particularly useful phosphors are those containing doped or undoped tantalum such as YTaO4, YTaO4:Nb, Y(Sr)TaO4, and Y(Sr)TaO4:Nb. These phosphors are described in U.S. Pat. No. 4,226,653 (Brixner), U.S. Pat. No. 5,064,729 (Zegarski), U.S. Pat. No. 5,250,366 (Nakajima et al.), and U.S. Pat. No. 5,626,957 (Benso et al.), all incorporated herein by reference.
Other useful phosphors are alkaline earth metal phosphors that can be the products of firing starting materials comprising optional oxide and a combination of species characterized by the following formula (2):
MFX1xe2x88x92zIzuMaXa:yA:eQ:tDxe2x80x83xe2x80x83(2)
wherein xe2x80x9cMxe2x80x9d is magnesium (Mg), calcium (Ca), strontium (Sr), or barium (Ba), xe2x80x9cFxe2x80x9d is fluoride, xe2x80x9cXxe2x80x9d is chloride (Cl) or bromide (Br), xe2x80x9cIxe2x80x9d is iodide, Ma is sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs), Xa is fluoride (F), chloride (Cl), bromide (Br), or iodide (I), xe2x80x9cAxe2x80x9d is europium (Eu), cerium (Ce), samarium (Sm), or terbium (Th), xe2x80x9cQxe2x80x9d is BeO, MgO, CaO, SrO, BaO, ZnO, Al2O3, La2O3, In2O3, SiO2, TiO2, ZrO2, GeO2, SnO2,:Nb2O5, Ta2O5, or ThO2, xe2x80x9cDxe2x80x9d is vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), or nickel (Ni). The numbers in the noted formula are the following: xe2x80x9czxe2x80x9d is 0 to 1, xe2x80x9cuxe2x80x9d is from 0 to 1, xe2x80x9cyxe2x80x9d is from 1xc3x9710xe2x88x924 to 0.1, xe2x80x9cexe2x80x9d is from 0 to 1, and xe2x80x9ctxe2x80x9d is from 0 to 0.01. These definitions apply wherever they are found in this application unless specifically stated to the contrary. It is also contemplated that xe2x80x9cMxe2x80x9d, xe2x80x9cXxe2x80x9d, xe2x80x9cAxe2x80x9d, and xe2x80x9cDxe2x80x9d represent multiple elements in the groups identified above.
Storage phosphors can also be used in the practice of this invention. Various storage phosphors are described for example, in U.S. Pat. No. 5,464,568 (noted above), incorporated herein by reference. Such phosphors include divalent alkaline earth metal fluorohalide phosphors that may contain iodide are the product of firing an intermediate, comprising oxide and a combination of species characterized by the following formula (3):
xe2x80x83(Ba1xe2x88x92axe2x88x92bxe2x88x92cMgaCabSrc)FX1xe2x88x92zIzrMaXa:yAxe2x80x83xe2x80x83(3)
wherein X, Ma, Xa, A, z, and y have the same meanings as for formula (2) and the sum of a, b, and c is from 0 to 4, and r is from 10xe2x88x926 to 0.1. Some embodiments of these phosphors are described in more detail in U.S. Pat. No. 5,464,568 (noted above).
Still other storage phosphors are described in U.S. Pat. No. 4,368,390 (Takahashi et al.), incorporated herein by reference, and include divalent europium and other rare earth activated alkaline earth metal halides and rare earth element activated rare earth oxyhalides, as described in more detail above.
Examples of useful phosphors include: SrS:Ce,SM, SrS:Eu,Sm, ThO2:Er, La2O2S:Eu,Sm, ZnS:Cu,Pb, and others described in U.S. Pat. No. 5,227,253 (Takasu et al.), incorporated herein by reference.
The one or more phosphors used in the practice of this invention are present in the photothermographic materials in an amount of at least 0.1 mole per mole, and preferably from about 0.5 to about 20 mole, per mole of total silver in the photothermographic material. Generally, the amount of total silver is at least 0.002 mol/m2.
Because of the size of the phosphors used in the invention, generally the layers in which they are incorporated (usually one or more emulsion layers), have a dry coating weight of at least 5 g/m2, and preferably from about 5 g/m2, to about 200 g/m2. Most preferably, the one or more phosphors and the photosensitive silver halide are incorporated within the same imaging layer that has a dry coating weight within the noted preferred range.
Thus, one preferred embodiment of the present invention is an X-radiation sensitive photothermographic material comprising a support having on one side thereof, a photothermographic imaging layer having a dry coating weight of from about 5 to about 200 g/m2, and a surface protective layer, the imaging layer comprising a binder and in reactive association:
a. a photosensitive silver halide,
b. a non-photosensitive source of reducible silver ions,
c. a reducing composition for the reducible silver ions, and
d. a phosphor that is sensitive to X-radiation and is present in an amount of from about 0.1 to about 20 mole per mole of total silver,
the phosphor being one or more of YTaO4, YTaO4:Nb, Y(Sr)TaO4, and Y(Sr)TaO4:Nb.
Reducing Agents
The reducing agent (or reducing agent composition comprising two or more components) for the source of reducible silver ions can be any material, preferably an organic material, that can reduce silver (I) ion to metallic silver. Conventional photographic developers such as methyl gallate, hydroquinone, substituted hydroquinones, hindered phenols, amidoximes, azines, catechol, pyrogallol, ascorbic acid (and derivatives thereof), leuco dyes and other materials readily apparent to one skilled in the art can be used in this manner as described for example in U.S. Pat. No. 6,020,117 (Bauer et al.), incorporated herein by reference.
In some instances, the reducing agent composition comprises two or more components such as a hindered phenol developer and a co-developer that can be chosen from the various classes of reducing agents described below. Ternary developer mixtures involving the further addition of contrast enhancing agents are also useful. Such contrast enhancing agents can be chosen from the various classes of reducing agents described below.
Hindered phenol reducing agents are preferred (alone or in combination with one or more high contrast co-developing agents and contrast enhancing agents). These are compounds that contain only one hydroxy group on a given phenyl ring and have at least one additional substituent located ortho to the hydroxy group. Hindered phenol developers may contain more than one hydroxy group as long as each hydroxy group is located on different phenyl rings. Hindered phenol developers include, for example, binaphthols (that is dihydroxybinaphthyls), biphenols (that is dihydroxybiphenyls), bis(hydroxynaphthlyl)methanes, bis(hydroxyphenyl)methanes, hindered phenols, and hindered naphthols each of which may be variously substituted.
Representative binaphthols include, but are not limited, to 1,1xe2x80x2-bi-2-naphthol, 1,1xe2x80x2-bi-4-methyl-2-naphthol and 6,6xe2x80x2-dibromo-bi-2-naphthol. For additional compounds see U.S. Pat. No. 3,094,417 (Workman) and U.S. Pat. No. 5,262,295 (Tanaka et al.), both incorporated herein by reference.
Representative biphenols include, but are not limited, to 2,2xe2x80x2-dihydroxy-3,3xe2x80x2-di-t-butyl-5,5-dimethylbiphenyl, 2,2xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetra-t-butylbiphenyl, 2,2xe2x80x2-dihydroxy-3,3xe2x80x2-di-t-butyl-5,5xe2x80x2-dichlorobiphenyl, 2-(2-hydroxy-3-t-butyl-5-methylphenyl)-4-methyl-6-n-hexylphenol, 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetra-t-butylbiphenyl and 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetramethylbiphenyl. For additional compounds see U.S. Pat. No. 5,262,295 (noted above).
Representative bis(hydroxynaphthyl)methanes include, but are not limited to, 4,4xe2x80x2-methylenebis(2-methyl-1-naphthol). For additional compounds see U.S. Pat. No. 5,262,295 (noted above).
Representative bis(hydroxyphenyl)methanes include, but are not limited to, bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane (CAO-5), 1,1xe2x80x2-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane (NONOX or PERMANAX WSO), 1,1xe2x80x2-bis(3,5-di-t-butyl-4-hydroxyphenyl)methane, 2,2xe2x80x2-bis(4-hydroxy-3-methylphenyl)propane, 4,4xe2x80x2-ethylidene-bis(2-t-butyl-6-methylphenol), 2,2xe2x80x2-isobutylidene-bis(4,6-dimethylphenol) (LOWINOX 221B46), and 2,2xe2x80x2-bis(3,5-dimethyl-4-hydroxyphenyl)propane. For additional compounds see U.S. Pat. No. 5,262,295 (noted above).
Representative hindered phenols include, but are not limited to, 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,4-di-t-butylphenol, 2,6-dichlorophenol, 2,6-dimethylphenol and 2-t-butyl-6-methylphenol.
Representative hindered naphthols include, but are not limited to, 1-naphthol, 4-methyl-1-naphthol, 4-methoxy-1-naphthol, 4-chloro-1-naphthol and 2-methyl-1-naphthol. For additional compounds see U.S. Pat. No. 5,262,295 (noted above).
More specific alternative reducing agents that have been disclosed in dry silver systems including amidoximes such as phenylamidoxime, 2-thienyl-amidoxime and p-phenoxyphenylamidoxime, azines (for example, 4-hydroxy-3,5-dimethoxybenzaldehydrazine), a combination of aliphatic carboxylic acid aryl hydrazides and ascorbic acid, such as 2,2xe2x80x2-bis(hydroxymethyl)-propionyl-xcex2-phenyl hydrazide in combination with ascorbic acid, a combination of polyhydroxybenzene and hydroxylamine, a reductone and/or a hydrazine [for example, a combination of hydroquinone and bis(ethoxyethyl)hydroxylamine], piperidinohexose reductone or formyl-4-methylphenylhydrazine, hydroxamic acids (such as phenylhydroxamic acid, p-hydroxyphenylhydroxamic acid, and o-alanine-hydroxamic acid), a combination of azines and sulfonamidophenols (for example, phenothiazine and 2,6-dichloro-4-benzenesulfonamidophenol), xcex1-cyanophenyl-acetic acid derivatives (such as ethyl xcex1-cyano-2-methylphenylacetate and ethyl xcex1-cyanophenylacetate), bis-o-naphthols [such as 2,2xe2x80x2-dihydroxyl-1-binaphthyl, 6,6xe2x80x2-dibromo-2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphthyl, and bis(2-hydroxy-1-naphthyl)-methane], a combination of bis-o-naphthol and a 1,3-dihydroxybenzene derivative (for example, 2,4-dihydroxybenzophenone or 2,4-dihydroxyacetophenone), 5-pyrazolones such as 3-methyl-1-phenyl-5-pyrazolone, reductones (such as dimethylaminohexose reductone, anhydrodihydro-aminohexose reductone and anhydrodihydro-piperidone-hexose reductone), sulfonamidophenol reducing agents (such as 2,6-dichloro-4-benzenesulfonamido-phenol, and p-benzenesulfonamidophenol), 2-phenylindane-1,3-dione and similar compounds, chromans (such as 2,2-dimethyl-7-t-butyl-6-hydroxychroman), 1,4-dihydropyridines (such as 2,6-dimethoxy-3,5-dicarbethoxy-1,4-dihydropyridine), ascorbic acid derivatives (such as 1-ascorbylpalmitate, ascorbylstearate and unsaturated aldehydes and ketones), 3-pyrazolidones, and certain indane-1,3-diones.
An additional class of reducing agents that can be used as developers are substituted hydrazines including the sulfonyl hydrazides described in U.S. Pat. No. 5,464,738 (Lynch et al.). Still other useful reducing agents are described, for example, in U.S. Pat. No. 3,074,809 (Owen), U.S. Pat. No. 3,094,417 (Workman), U.S. Pat. No. 3,080,254 (Grant, Jr.) and U.S. Pat. No. 3,887,417 (Klein et al.). Auxiliary reducing agents may be useful as described in U.S. Pat. No. 5,981,151 (Leenders et al.). All of these patents are incorporated herein by reference.
Useful co-developer reducing agents can also be used as described for example, in copending U.S. Ser. No. 09/239,182 (filed Jan. 28, 1999 by Lynch and Skoog), incorporated herein by reference. Examples of these compounds include, but are not limited to, 2,5-dioxo-cyclopentane carboxaldehydes, 5-(hydroxymethylene)-2,2-dimethyl-1,3-dioxane-4,6-diones, 5-(hydroxymethylene)-1,3-dialkylbarbituric acids, and 2-(ethoxymethylene)-1H-indene-1,3(2H)-diones.
Additional classes of reducing agents that can be used as co-developers are trityl hydrazides and formyl phenyl hydrazides as described in U.S. Pat. No. 5,496,695 (Simpson et al.), 2-substituted malondialdehyde compounds as described in U.S. Pat. No. 5,654,130 (Murray), and 4-substituted isoxazole compounds as described in U.S. Pat. No. 5,705,324 (Murray). Additional developers are described in U.S. Pat. No. 6,100,022 (Inoue et al.). All of the patents above are incorporated herein by reference.
Yet another class of co-developers are substituted acrylonitrile compounds that can be represented by structure III as follows:
H(Rxe2x80x2)Cxe2x95x90C(R)CNxe2x80x83xe2x80x83III
wherein R is a substituted or unsubstituted aryl group of 6 to 14 carbon atoms in the single or fused ring structure (such as phenyl, naphthyl, p-methylphenyl, p-chlorophenyl, 4-pyridinyl and o-nitrophenyl groups) or an electron withdrawing group (such as a halo atom, cyano group, carboxy group, ester group and phenylsulfonyl group). Rxe2x80x2 is a halo group (such as fluoro, chloro and bromo), hydroxy or metal salt thereof, a thiohydrocarbyl group, an oxyhydroxycarbyl group, or a substituted or unsubstituted 5- or 6-membered aromatic heterocyclic group having only carbon atoms and 1 to 4 nitrogen atoms in the central ring (with or without fused rings attached), and being attached through a non-quaternary ring nitrogen atom (such as pyridyl, furyl, diazolyl, triazolyl, pyrrolyl, tetrazolyl, benzotriazolyl, benzopyrrolyl and quinolinyl groups). Further details of these compounds and their preparation can be found in U.S. Pat. No. 5,635,339 (Murray) and U.S. Pat. No. 5,545,515 (Murray et al.), both incorporated herein by reference.
Examples of such compounds include, but are not limited to, the compounds identified as HET-01 and HET-02 in U.S. Pat. No. 5,635,339 (noted above) and CN-01 through CN-13 in U.S. Pat. No. 5,545,515 (noted above). Particularly useful compounds of this type are (hydroxymethylene)cyanoacetates and their metal salts.
Various contrast enhancers can be used in some photothermographic materials with specific co-developers. Examples of useful contrast enhancers include, but are not limited to, hydroxylamines (including hydroxylamine and alkyl- and aryl-substituted derivatives thereof), alkanolamines and ammonium phthalamate compounds as described for example, in U.S. Pat. No. 5,545,505 (Simpson), hydroxamic acid compounds as described for example, in U.S. Pat. No. 5,545,507 (Simpson et al.), N-acylhydrazine compounds as described for example, in U.S. Pat. No. 5,558,983 (Simpson et al.), and hydrogen atom donor compounds as described in U.S. Pat. No. 5,637,449 (Harring et al.). All of the above patents are incorporated herein by reference.
The reducing agent (or mixture thereof) described herein is generally present as 1 to 10% (dry weight) of the emulsion layer. In multilayer constructions, if the reducing agent is added to a layer other than an emulsion layer, slightly higher proportions, of from about 2 to 15 weight % may be more desirable. Any co-developers may be present generally in an amount of from about 0.001% to about 1.5% (dry weight) of the emulsion layer coating.
For color imaging materials (for example, monochrome, dichrome, or full color images), one or more reducing agents can be used that can be oxidized directly or indirectly to form or release one or more dyes.
The dye-forming or releasing compound may be any colored, colorless or lightly colored compound that can be oxidized to a colored form, or to release a preformed dye when heated, preferably to a temperature of from about 80xc2x0 C. to about 250xc2x0 C. for a duration of at least 1 second. When used with a dye- or image-receiving layer, the dye can diffuse through the imaging layers and interlayers into the image-receiving layer of the photothermographic material.
Leuco dyes or xe2x80x9cblockedxe2x80x9d leuco dyes are one class of dye-forming compounds (or xe2x80x9cblockedxe2x80x9d dye-forming compounds) that form and release a dye upon oxidation by silver ion to form a visible color image in the practice of the present invention. Leuco dyes are the reduced form of dyes that are generally colorless or very lightly colored in the visible region (optical density of less than 0.2). Thus, oxidation provides a color change that is from colorless to colored, or an optical density increase of at least 0.2 units or a substantial change in hue.
Representative classes of useful leuco dyes include, but are not limited to, chromogenic leuco dyes (such as indoaniline, indophenol, or azomethine dyes), imidazole leuco dyes such as 2-(3,5-di-t-butyl-4-hydroxyphenyl)-4,5-diphenylimidazole as described for example in U.S. Pat. No. 3,985,565 (Gabrielson et al.), dyes having an azine, diazine, oxazine, or thiazine nucleus such as those described for example in U.S. Pat. No. 4,563,415 (Brown et al.), U.S. Pat. No. 4,622,395 (Bellus et al.), U.S. Pat. No. 4,710,570 (Thien), and U.S. Pat. No. 4,782,010 (Mader et al.), and benzlidene leuco compounds as described for example in U.S. Pat. No. 4,932,792 (Grieve et al.), all incorporated herein by reference. Further details about the chromogenic leuco dyes noted above can be obtained from U.S. Pat. No. 5,491,059 (noted above, Column 13) and references noted therein.
Another useful class of leuco dyes are what are known as xe2x80x9caldazinexe2x80x9d and xe2x80x9cketazinexe2x80x9d leuco dyes, which are described for example in U.S. Pat. No. 4,587,211 (Ishida et al.) and U.S. Pat. No. 4,795,697 (Vogel et al.), both incorporated herein by reference.
Still another useful class of dye-releasing compounds are those that release diffusible dyes upon oxidation. These are known as preformed dye release (PDR) or redox dye release (RDR) compounds. In such compounds, the reducing agents release a mobile preformed dye upon oxidation. Examples of such compounds are described in U.S. Pat. No. 4,981,775 (Swain), incorporated herein by reference.
Further, other useful image-forming compounds are those in which the mobility of a dye moiety changes as a result of an oxidation-reduction reaction with silver halide, or a nonphotosensitive silver salt at high temperature, as described for example in JP Kokai 165,054/84.
Still further the reducing agent can be a compound that releases a conventional photographic dye forming color coupler or developer upon oxidation as is known in the photographic art.
The dyes that are formed or released can be the same in the same or different imaging layers. A difference of at least 60 nm in reflective maximum absorbance is preferred. More preferably, this difference is from about 80 to about 100 nm. Further details about the various dye absorbances are provided in U.S. Pat. No. 5,491,059 (noted above, Col. 14).
The total amount of one or more dye-forming or releasing compound that can be incorporated into the photothermographic materials of this invention is generally from about 0.5 to about 25 weight % of the total weight of each imaging layer in which they are located. Preferably, the amount in each imaging layer is from about 1 to about 10 weight %, based on the total dry layer weight. The useful relative proportions of the leuco dyes would be readily known to a skilled worker in the art.
Imaging Precursor Emulsions
As pointed out above, this invention also provides various imaging precursor emulsions that can be formulated and used to prepare the photothermographic materials of this invention. Such imaging precursor emulsions comprise one or more phosphors as described above, in suitable amounts, and two or more of the essential imaging components: that is, one or more photosensitive silver halides, one or more non-photosensitive sources of reducible silver ions, and one or more reducing compositions for the reducible silver ions, all of which are described above.
Thus, one such imaging precursor emulsion can comprise one or more phosphors in combination with one or more photosensitive silver halides and one or more non-photosensitive sources of reducible silver ions.
Another suitable imaging precursor emulsion can comprise one or more phosphors in combination with one or more photosensitive silver halides and one or more reducing compositions for the reducible silver ions.
Still another useful imaging precursor emulsion can comprise one or more phosphors in combination with one or more non-photosensitive sources of reducible silver ions and one or more reducing compositions for the reducible silver ions.
Yet another useful imaging precursor emulsion can include one or more phosphors in combination with one or more photosensitive silver halides, one or more non-photosensitive sources of reducible silver ions, and one or more reducing compositions for the reducible silver ions.
The various amounts of each essential imaging component in the various imaging precursor emulsions would be readily apparent to one skilled in the art from the teaching provided above for the individual components.
In addition, each imaging precursor emulsion can include various addenda as described in the following disclosure. Preferably, the imaging precursor emulsions comprise one or more binders (particularly hydrophobic binders) as described below.
Other Addenda
The photothermographic materials of this invention can also contain other additives such as shelf-life stabilizers, toners, antifoggants, contrast enhancers, development accelerators, acutance dyes, post-processing stabilizers or stabilizer precursors, and other image-modifying agents as would be readily apparent to one skilled in the art.
The photothermographic materials can be further protected against the production of fog and can be stabilized against loss of sensitivity during storage. While not necessary for the practice of the invention, it may be advantageous to add mercury (II) salts to the emulsion layer(s) as an antifoggant. Preferred mercury (II) salts for this purpose are mercuric acetate and mercuric bromide. Other useful mercury salts include those described in U.S. Pat. No. 2,728,663 (Allen).
Other suitable antifoggants and stabilizers that can be used alone or in combination include thiazolium salts as described in U.S. Pat. No. 2,131,038 (Staud) and U.S. Pat. No. 2,694,716 (Allen), azaindenes as described in U.S. Pat. No. 2,886,437 (Piper), triazaindolizines as described in U.S. Pat. No. 2,444,605 (Heimbach), the urazoles described in U.S. Pat. No. 3,287,135 (Anderson), sulfocatechols as described in U.S. Pat. No. 3,235,652 (Kennard), the oximes described in GB 623,448 (Carrol et al.), polyvalent metal salts as described in U.S. Pat. No. 2,839,405 (Jones), thiuronium salts as described in U.S. Pat. No. 3,220,839 (Herz), palladium, platinum, and gold salts as described in U.S. Pat. No. 2,566,263 (Trirelli) and U.S. Pat. No. 2,597,915 (Damshroder), and 2-(tribromomethylsulfonyl)quinoline compounds as described in U.S. Pat. No. 5,460,938 (Kirk et al.). Stabilizer precursor compounds capable of releasing stabilizers upon application of heat during development can also be used. Such precursor compounds are described in for example, U.S. Pat. No. 5,158,866 (Simpson et al.), U.S. Pat. No. 5,175,081 (Krepski et al.), U.S. Pat. No. 5,298,390 (Sakizadeh et al.), and U.S. Pat. No. 5,300,420 (Kenney et al.).
In addition, certain substituted-sulfonyl derivatives of benzotriazoles (for example alkylsulfonylbenzotriazoles and arylsulfonylbenzotriazoles) have been found to be useful stabilizing compounds (such as for post-processing print stabilizing), as described in U.S. Pat. No. 6,171,767B1 (Kong et al).
Furthermore, other useful antifoggants/stabilizers are described in U.S. Pat. No. 6,083,681 (Lynch et al.), incorporated herein by reference.
Other antifoggants are hydrobromic acid salts of heterocyclic compounds (such as pyridinium hydrobromide perbromide) as described, for example, in U.S. Pat. No. 5,028,523 (Skoug), compounds having xe2x80x94SO2CBr3 groups as described for example in U.S. Pat. No. 5,594,143 (Kirk et al.) and U.S. Pat. No. 5,374,514 (Kirk et al.), benzoyl acid compounds as described, for example, in U.S. Pat. No. 4,784,939 (Pham), substituted propenenitrile compounds as described, for example, in U.S. Pat. No. 5,686,228 (Murray et al.), silyl blocked compounds as described, for example, in U.S. Pat. No. 5,358,843 (Sakizadeh et al.), vinyl sulfones as described, for example, in EP-A-0 600,589 (Philip, Jr. et al.) and EP-A-0 600 586 (Philip, Jr. et al.), and tribromomethylketones as described, for example, in EP-A-0 600,587 (Oliff et al.).
Preferably, the photothermographic materials of this invention include one or more polyhalo antifoggants that include one or more polyhalo substituents including but not limited to, dichloro, dibromo, trichloro, and tribromo groups. The antifoggants can be aliphatic, alicyclic or aromatic compounds, including aromatic heterocyclic and carbocyclic compounds.
The use of xe2x80x9ctonersxe2x80x9d or derivatives thereof that improve the image is highly desirable. Preferably, if used, a toner can be present in an amount of about 0.01% by weight to about 10%, and more preferably about 0.1% by weight to about 10% by weight, based on the total dry weight of the layer in which it is included. Toners may be incorporated in the photothermographic emulsion layer or in an adjacent layer. Toners are well known materials in the thermographic and photothermographic art, as shown in U.S. Pat. No. 3,080,254 (Grant, Jr.), U.S. Pat. No. 3,847,612 (Winslow), U.S. Pat. No. 4,123,282 (Winslow), U.S. Pat. No. 4,082,901 (Laridon et al.), U.S. Pat. No. 3,074,809 (Owen), U.S. Pat. No. 3,446,648 (Workman), U.S. Pat. No. 3,844,797 (Willems et al.), U.S. Pat. No. 3,951,660 (Hagemann et al.), U.S. Pat. No. 5,599,647 (Defieuw et al.) and GB 1,439,478 (Agfa-Gevaert).
Examples of toners include, but are not limited to, phthalimide and N-hydroxyphthalimide, cyclic imides (such as succinimide), pyrazoline-5-ones, quinazolinone, 1-phenylurazole, 3-phenyl-2-pyrazoline-5-one, and 2,4-thiazolidinedione, naphthalimides (such as N-hydroxy-1,8-naphthalimide), cobalt complexes [such as hexaaminecobalt(3+) trifluoroacetate], mercaptans (such as 3-mercapto-1,2,4-triazole, 2,4-dimercaptopyrimidine, 3-mercapto-4,5-diphenyl-1,2,4-triazole and 2,5-dimercapto-1,3,4-thiadiazole), N-(aminomethyl)aryldicarboximides [such as (N,N-dimethylaminomethyl)phthalimide, and N-(dimethylaminomethyl)naphthalene-2,3-dicarboximide, a combination of blocked pyrazoles, isothiuronium derivatives, and certain photobleach agents [such as a combination of N,Nxe2x80x2-hexamethylene-bis(1-carbamoyl-3,5-dimethyl-pyrazole), 1,8-(3,6-diazaoctane)bis(isothiuronium)trifluoroacetate, and 2-(tribromomethylsulfonyl benzothiazole)], merocyanine dyes {such as 3-ethyl-5-[(3-ethyl-2-benzothiazolinylidene)-1-methyl-ethylidene]-2-thio-2,4-o-azolidinedione}, phthalazine and derivatives thereof [such as those described in U.S. Pat. No. 6,146,822 (Asanuma et al.)], phthalazinone and phthalazinone derivatives, or metal salts or these derivatives [such as 4-(1-naphthyl)phthalazinone, 6-chlorophthalazinone, 5,7-dimethoxyphthalazinone, and 2,3-dihydro-1,4-phthalazinedione], a combination of phthalazine (or derivative thereof) plus one or more phthalic acid derivatives (such as phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, and tetrachlorophthalic anhydride), quinazolinediones, benzoxazine or naphthoxazine derivatives, rhodium complexes functioning not only as tone modifiers but also as sources of halide ion for silver halide formation in situ [such as ammonium hexachlororhodate (III), rhodium bromide, rhodium nitrate, and potassium hexachlororhodate (III)], benzoxazine-2,4-diones (such as 1,3-benzoxazine-2,4-dione, 8-methyl-1,3-benzoxazine-2,4-dione and 6-nitro-1,3-benzoxazine-2,4-dione), pyrimidines and asym-triazines (such as 2,4-dihydroxypyrimidine, 2-hydroxy-4-aminopyrimidine and azauracil) and tetraazapentalene derivatives [such as 3,6-dimercapto-1,4-diphenyl-1H,4H-2,3a,5,6a-tetraazapentalene and 1,4-di-(o-chlorophenyl)-3,6-dimercapto-1H,4H-2,3a,5,6a-tetraazapentalene].
Phthalazines and phthalazine derivatives [such as those described in U.S. Pat. No. 6,146,822 (noted above), incorporated herein by reference] are particularly useful toners.
Binders
The photosensitive silver halide, the non-photosensitive source of reducible silver ions, the reducing agent composition, the phosphor and any other additives used in the present invention are generally added to one or more binders that are either hydrophilic or hydrophobic. Thus, either aqueous- or solvent-based formulations can be used to prepare the photothermographic materials of this invention. Mixtures of either or both types of binders can also be used. It is preferred that the binder be selected from hydrophobic polymeric materials, such as, for example, natural and synthetic resins that are sufficiently polar to hold the other ingredients in solution or suspension.
Examples of typical hydrophobic binders include, but are not limited to, polyvinyl acetals, polyvinyl chloride, polyvinyl acetate, cellulose acetate, cellulose acetate butyrate, polyolefins, polyesters, polystyrenes, polyacrylonitrile, polycarbonates, methacrylate copolymers, maleic anhydride ester copolymers, butadiene-styrene copolymers, and other materials readily apparent to one skilled in the art. Copolymers (including terpolymers) are also included in the definition of polymers. The polyvinyl acetals (such as polyvinyl butyral and polyvinyl formal) and vinyl copolymers (such as polyvinyl acetate and polyvinyl chloride) are particularly preferred. Particularly suitable binders are polyvinyl butyral resins that are available as BUTVAR(copyright) B79 (Solutia, Inc.) and Pioloform BS-18 or Pioloform BL-16 (Wacker Chemical Company).
Examples of useful hydrophilic binders include, but are not limited to, gelatin and gelatin-like derivatives (hardened or unhardened), cellulosic materials such as cellulose acetate, cellulose acetate butyrate, hydroxymethyl cellulose, acrylamide/methacrylamide polymers, acrylic/methacrylic polymers polyvinyl pyrrolidones, polyvinyl acetates, polyvinyl alcohols, and polysaccharides (such as dextrans and starch ethers).
Hardeners for various binders may be present if desired. Useful hardeners are well known and include diisocyanate compounds as described for example in EP-0 600 586B1 and vinyl sulfone compounds as described in EP-0 600 589B1.
Where the proportions and activities of the photothermographic materials require a particular developing time and temperature, the binder(s) should be able to withstand those conditions. Generally, it is preferred that the binder not be decomposed or lose its structural integrity at 120xc2x0 C. for 60 seconds. It is more preferred that it not be decomposed or lose its structural integrity at 177xc2x0 C. for 60 seconds.
The polymer binder(s) is used in an amount sufficient to carry the components dispersed therein. The effective range can be appropriately determined by one skilled in the art. Preferably, a binder is used at a level of about 10% by weight to about 90% by weight, and more preferably at a level of about 20% by weight to about 70% by weight, based on the total dry weight of the layer in which it is included.
Support Materials
The photothermographic materials of this invention can be prepared using a polymeric support that is preferably a flexible, transparent film that has any desired thickness and is composed of one or more polymeric materials, depending upon their use. The supports are generally transparent (especially if the material is used as a photomask) or at least translucent, but in some instances, opaque supports may be useful. They are required to exhibit dimensional stability during thermal development and to have suitable adhesive properties with overlying layers. Useful polymeric materials for making such supports include, but are not limited to, polyesters (such as polyethylene terephthalate and polyethylene naphthalate), cellulose acetate and other cellulose esters, polyvinyl acetal, polyolefins (such as polyethylene and polypropylene), polycarbonates, and polystyrenes (and polymers of styrene derivatives). Preferred supports are composed of polymers having good heat stability, such as polyesters and polycarbonates. Polyethylene terephthalate film is the most preferred support. Various support materials are described, for example, in Research Disclosure, August 1979, item 18431. A method of making dimensionally stable polyester films is described in Research Disclosure, September, 1999, item 42536.
Opaque supports can also be used such as dyed polymeric films and resin-coated papers that are stable to high temperatures.
Support materials can contain various colorants, pigments, antihalation or acutance dyes if desired. Support materials may be treated using conventional procedures (such as corona discharge) to improve adhesion of overlying layers, or subbing or other adhesion-promoting layers can be used. Useful subbing layer formulations include those conventionally used for photographic materials such as vinylidene halide polymers.
Photothermographic Formulations
The formulation for the photothermographic emulsion layer(s) is preferably prepared by dissolving and/or dispersing a hydrophobic binder, the photothermographic emulsion (generally including the photosensitive silver halide and the non-photosensitive source of reducible silver ions) the reducing composition, the phosphor, and optional addenda in an organic solvent, such as toluene, 2-butanone (methyl ethyl ketone), acetone, or tetrahydrofuran. As noted above, these components can be distributed between two or more imaging layers. In some instances, some of the components can be formulated in a topcoat formulation and allowed to migrate into lower imaging layers.
Alternatively, these components can be formulated with a hydrophilic binder in water or water-organic solvent mixtures to provide aqueous-based coating formulations.
Photothermographic materials can also contain plasticizers and lubricants such as polyalcohols and diols of the type described in U.S. Pat. No. 2,960,404 (Milton et al.), fatty acids or esters such as those described in U.S. Pat. No. 2,588,765 (Robijns) and U.S. Pat. No. 3,121,060 (Duane), and silicone resins such as those described in GB 955,061 (DuPont). The materials can also contain matting agents such as starch, titanium dioxide, zinc oxide, silica, and polymeric beads, including beads of the type described in U.S. Pat. No. 2,992,101 (Jelley et al.) and U.S. Pat. No. 2,701,245 (Lynn). Polymeric fluorinated surfactants may also be useful in one or more layers of the imaging materials for various purposes, such as improving coatability and optical density uniformity as described in U.S. Pat. No. 5,468,603 (Kub).
EP-A-0 792 476 (Geisler et al.) describes various means of modifying the photothermographic materials to reduce what is known as the xe2x80x9cwoodgrainxe2x80x9d effect, or uneven optical density. This effect can be reduced or eliminated by several means, including treatment of the support, adding matting agents to the topcoat, using acutance dyes in certain layers, or other procedures described in the noted publication.
The photothermographic materials can include antistatic or conducting layers. Such layers may contain soluble salts (for example, chlorides or nitrates), evaporated metal layers, or ionic polymers such as those described in U.S. Pat. No. 2,861,056 (Minsk) and U.S. Pat. No. 3,206,312 (Sterman et al.), or insoluble inorganic salts such as those described in U.S. Pat. No. 3,428,451 (Trevoy), electroconductive underlayers such as those described in U.S. Pat. No. 5,310,640 (Markin et al.), electronically-conductive metal antimonate particles such as those described in U.S. Pat. No. 5,368,995 (Christian et al.), and electrically-conductive metal-containing particles dispersed in a polymeric binder such as those described in EP-A-0 678 776 (Melpolder et al.). Other antistatic agents are well known in the art.
The photothermographic materials can be constructed of one or more layers on a support. Single layer materials should contain the photosensitive silver halide, the non-photosensitive source of reducible silver ions, the reducing composition, the binder, the phosphor, as well as optional materials such as toners, acutance dyes, coating aids and other adjuvants.
Two-layer constructions comprising a single imaging layer coating containing all the ingredients and a protective topcoat are generally found in the materials of this invention. However, two-layer constructions containing photosensitive silver halide and non-photosensitive source of reducible silver ions in one imaging layer (usually the layer adjacent to the support) and the reducing composition and other ingredients (including phosphor) in the second imaging layer or distributed between both layers are also envisioned. Preferably, in such constructions, the phosphor is in the same layer as the photosensitive silver halide.
Layers to promote adhesion of one layer to another are also known, as described for example, in U.S. Pat. No. 5,891,610 (Bauer et al.), U.S. Pat. No. 5,804,365 (Bauer et al.), and U.S. Pat. No. 4,741,992 (Przezdziecki). Adhesion can also be promoted using specific polymeric adhesive materials as described for example, in U.S. Pat. No. 5,928,857 (Geisler et al.).
Photothermographic formulations described herein can be coated by various coating procedures including wire wound rod coating, dip coating, air knife coating, curtain coating, slide coating, or extrusion coating using hoppers of the type described in U.S. Pat. No. 2,681,294 (Beguin). Layers can be coated one at a time, or two or more layers can be coated simultaneously by the procedures described in U.S. Pat. No. 2,761,791 (Russell), U.S. Pat. No. 4,001,024 (Dittman et al.), U.S. Pat. No. 4,569,863 (Keopke et al.), U.S. Pat. No. 5,340,613 (Hanzalik et al.), U.S. Pat. No. 5,405,740 (LaBelle), U.S. Pat. No. 5,415,993 (Hanzalik et al.), U.S. Pat. No. 5,525,376 (Leonard), U.S. Pat. No. 5,733,608 (Kessel et al.), U.S. Pat. No. 5,849,363 (Yapel et al.), U.S. Pat. No. 5,843,530 (Jerry et al.), U.S. Pat. No. 5,861,195 (Bhave et al.), and GB 837,095 (Ilford). A typical coating gap for the emulsion layer can be from about 10 to about 750 xcexcm, and the layer can be dried in forced air at a temperature of from about 20xc2x0 C. to about 100xc2x0 C. It is preferred that the thickness of the layer be selected to provide maximum image densities greater than about 0.2, and more preferably, from about 0.5 to 5.0 or more, as measured by a MacBeth Color Densitometer Model TD 504.
When the layers are coated simultaneously using various coating techniques, a xe2x80x9ccarrierxe2x80x9d layer formulation comprising a single-phase mixture of the two or more polymers, described above, may be used. Such formulations are described in copending and commonly assigned U.S. Ser. No. 09/510,648 (filed Feb. 23, 2000 by Ludemann, LaBelle, Geisler, Warren, Crump, and Bhave), incorporated herein by reference.
Mottle and other surface anomalies can be reduced in the materials of this invention by incorporation of a fluorinated polymer as described for example, in U.S. Pat. No. 5,532,121 (Yonkoski et al.) or by using particular drying techniques as described, for example, in U.S. Pat. No. 5,621,983 (Ludemann et al.).
Preferably, two or more layers are applied to a film support using slide coating. The first layer can be coated on top of the second layer while the second layer is still wet. The first and second fluids used to coat these layers can be the same or different organic solvents (or organic solvent mixtures).
While the first and second layers can be coated on one side of the film support, manufacturing methods can also include forming on the opposing or backside of said polymeric support, one or more additional layers, including an antihalation layer, an antistatic layer, or a layer containing a matting agent (such as silica), or a combination of such layers. It is also contemplated that the photothermographic materials of this invention can include emulsion layers on both sides of the support.
To promote image sharpness, photothermographic materials can contain one or more layers containing acutance and/or antihalation dyes. These dyes are chosen to have absorption close to the exposure wavelength and are designed to absorb scattered light. One or more antihalation dyes may be incorporated into one or more antihalation layers according to known techniques, as an antihalation backing layer, as an antihalation underlayer, or as an antihalation overcoat. Additionally, one or more acutance dyes may be incorporated into one or more frontside layers such as the photothermographic emulsion layer, primer layer, underlayer, or topcoat layer according to known techniques. It is preferred that the photothermographic materials of this invention contain an antihalation coating on the support opposite to the side on which the emulsion and topcoat layers are coated.
Dyes particularly useful as antihalation and acutance dyes include dihydroperimidine squaraine dyes having the nucleus represented by the following general structure: 
Details of such dyes having the dihydroperimidine squaraine nucleus and methods of their preparation can be found in U.S. Pat. No. 6,063,560 (Suzuki et al.) and U.S. Pat. No. 5,380,635 (Gomez et al.), both incorporated herein by reference. These dyes can also be used as acutance dyes in frontside layers of the materials of this invention. One particularly useful dihydroperimidine squaraine dye is cyclobutenediylium, 1,3-bis[2,3-dihydro-2,2-bis[[1-oxohexyl)oxy]methyl]-1H-perimidin-4-yl]-2,4-dihydroxy-, bis(inner salt).
Dyes particularly useful as antihalation dyes in a backside layer of the photothermographic material also include indolenine cyanine dyes having the nucleus represented by the following general structure: 
Details of such antihalation dyes having the indolenine cyanine nucleus and methods of their preparation can be found in EP-A-0 342 810 (Leichter), incorporated herein by reference. One particularly useful cyanine dye, compound (6) described therein, is 3H-Indolium, 2-[2-[2-chloro-3-[(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)ethylidene]-5-methyl-1-cyclohexen-1-yl]ethenyl]-1,3,3-trimethyl-, perchlorate.
It is also possible to employ acutance or antihalation dyes that will decolorize with heat during processing. Dyes and constructions employing these types of dyes are described in, for example, U.S. Pat. No. 5,135,842 (Kitchin et al.), U.S. Pat. No. 5,266,452 (Kitchin et al.), U.S. Pat. No. 5,314,795 (Helland et al.), and EP-A-0 911 693 (Sakurada et al.).
Imaging/Development
The photothermographic materials of the present invention can be imaged using any suitable X-radiation imaging source to provide a latent image. Suitable exposure means are well known and include medical, mammographic, dental, and industrial X-ray units.
When storage phosphors are incorporated within the photothermographic materials, the initial exposure to X-radiation is xe2x80x9cstoredxe2x80x9d within the phosphor particles. When the material is then later exposed a second time to stimulating electromagnetic radiation (usually to visible light or infrared radiation), the xe2x80x9cstoredxe2x80x9d energy is then released as an emission of visible or infrared radiation. The photothermographic materials may then be developed by heating. BaFBr disclosed herein is such a storage phosphor.
It may also be desirable to use the photothermographic materials of this invention in combination with one or more conventional fluorescent intensifying screens (also known as radiographic phosphor panels) or metal intensifying screens. Such screens are well known in the art [for example, U.S. Pat. No. 4,865,944 (Roberts et al.) and U.S. Pat. No. 5,021,327 (Bunch et al.)]. For example, a fluorescent intensifying screen can be positioned in xe2x80x9cfrontxe2x80x9d of the photothermographic material so exposing X-radiation passes through the screen before striking the photothermographic material. Other conventional arrangements of screens and photothermographic materials in imaging assemblies or cassettes would be readily apparent to a skilled artisan.
Heat development conditions will vary, depending on the construction used but will typically involve heating the imagewise exposed material at a suitably elevated temperature. Thus, the latent image can be developed by heating the exposed material at a moderately elevated temperature of, for example, from about 50xc2x0 C. to about 250xc2x0 C. (preferably from about 80xc2x0 C. to about 200xc2x0 C. and more preferably from about 100xc2x0 C. to about 200xc2x0 C.) for a sufficient period of time, generally from about 1 to about 120 seconds. Heating can be accomplished using any suitable heating means such as a hot plate, a steam iron, a hot roller or a heating bath.
In some methods, the development is carried out in two steps. Thermal development takes place at a higher temperature for a shorter time (for example, at about 150xc2x0 C. for up to 10 seconds), followed by thermal diffusion at a lower temperature (for example, at about 80xc2x0 C.) in the presence of a transfer solvent.
All materials used in the following examples are readily available from standard commercial sources, such as Aldrich Chemical Co. (Milwaukee Wis.) unless otherwise specified. All percentages are by weight unless otherwise indicated. The following additional terms and materials were used.
ACRYLOID(trademark) A-21 or PARALOID A-21 is an acrylic copolymer available from Rohm and Haas (Philadelphia, Pa.).
BUTVAR(copyright) B-79 is a polyvinyl butyral resin available from Solutia, Inc. (St. Louis, Mo.).
CAB 171-15S is a cellulose acetate butyrate resin available from Eastman Chemical Co. (Kingsport, Tenn.).
CBBA is chlorobenzoylbenzoic acid.
DESMODUR(copyright) N3300 is an aliphatic hexamethylene diisocyanate available from Bayer Chemicals (Pittsburgh, Pa.).
MEK is methyl ethyl ketone (or 2-butanone).
PERMANAX WSO (or NONOX) is 1,1-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane [CAS RN=7292-14-0] and is available from St-Jean PhotoChemicals, Inc. (Quebec, Canada).
Phosphors were obtained from Nichia America Corp. (Mountville, Pa.).
Phosphor P-1 is Gd2O2S:Tb. It is a green emitting phosphor.
Phosphor P-2 is Y(Sr)TaO4. It is an ultraviolet emitting phosphor.
Phosphor P-3 is Y(Sr)TaO4:Nb.
Phosphor P-4 is CaWO4.
Phosphor P-5 is BaFBr:Eu.
xe2x80x9cPHPxe2x80x9d is pyridinium hydrobromide perbromide.
Chemical Sensitizer A is 
Chemical Sensitizer B (CS-B) is Au(III)(terpyridine)Cl3. It is described in L. Hollis et al., J. Am. Chem. Soc., 1983, 105, 4293 and in U.S. Ser. No. 09/768,094 (noted above).
Spectral Sensitizing Dye A is 
Spectral Sensitizing Dye B is 
High contrast Compound HC-1 is described in U.S. Pat. No. 5,545,515 (noted above) and has the following structure: 
Vinyl Sulfone-1 (VS-1) is described in EP-0 600 589B1 and has the following structure: 
Antifoggant A is 2-(tribromomethylsulfonyl)quinoline and has the following structure: 
Antifoggant B is: 
Backcoat Dye BC-1 is cyclobutenediylium, 1,3-bis[2,3-dihydro-2,2-bis[[1-oxohexyl)oxy]methyl]-1H-perimidin-4-yl]-2,4-dihydroxy-, bis(inner salt). It is believed to have the structure shown below. 
The photothermographic emulsions were chemically sensitized according to procedures described in U.S. Pat. No. 5,891,615 (noted above), or U.S. Ser. No. 09/768,094 (noted above). In addition, some emulsions were prepared and evaluated without being spectrally sensitized. Others were spectrally sensitized to the wavelength of interest.
The following examples are provided to illustrate the practice of this invention, and are not intended to be limiting in any manner.